Method for improving appearance in composite color-plus-clear coatings and compositions for use therein

ABSTRACT

The invention provides composite color-plus-clear coatings having improved appearance, especially with respect to wrinkling, and to methods and compositions for providing such coatings. The method of the invention utilizes a second coating composition comprising (A) a film forming component comprising (a) a first component comprising a compound having appended thereto at least one carbamate or urea functional group, or a group convertible to a carbamate or urea group, and (b) a second component comprising a compound reactive with said carbamate or urea groups on component (a), (B) a cyclic anhydride, and (C) a catalyst.

FIELD OF THE INVENTION

This invention relates to composite color-plus-clear coatings havingimproved appearance, especially with respect to wrinkling and color, andto methods and compositions for providing such coatings. Moreparticularly, the invention relates to the use of certain acidanhydrides to prevent wrinkling in solvent borne clearcoats used overwater borne basecoats, especially anionically stabilized water bornebasecoats.

BACKGROUND OF THE INVENTION

Composite color-plus-clear coatings are widely utilized in the coatingsart. They are particularly desirable where exceptional gloss, depth ofcolor, distinctness of image, or special metallic effects are required.The automotive industry has made extensive use of color-plus-clearcomposite coatings for automotive body panels.

As used herein, the term "composite color-plus-clear" relates tocomposite coating systems requiring the application of a first coating,typically a colored basecoat coating, followed by the application of asecond coating, generally a clearcoat, over the noncured or "wet" firstcoating. The applied first and second coatings are then cured. Thus,such systems are often described as "wet on wet" or "two coat/one bake".Drying processes which fall short of complete cure may be used betweenthe application of the coatings.

Clearcoats used in color-plus-clear systems must have an extremely highdegree of clarity in order to achieve the desired visual effects. Highgloss coatings also require a low degree of visual aberrations at thesurface in order to achieve the desired visual effect such as highdistinctness of image (DOI). As a result, clearcoats of color-plus-clearsystems are especially susceptible to the phenomenon known asenvironmental etch, i.e., spots or marks on or in the clear finish thatoften cannot be rubbed out.

Although many compositions have been proposed for use as the clearcoatof a color-plus-clear composite coating, prior art clearcoat coatingsoften suffer from disadvantages such as coatability problems,compatibility problems with the colored basecoat, solubility problems,and/or insufficient resistance to environmental etch.

Clearcoat coating compositions exhibiting many advantages over prior artcompositions, especially with respect to environmental etch, weredisclosed in U.S. Pat. Nos. 5,474,811 and 5,356,669. The disclosed clearcoating compositions comprise a first component comprising a polymerbackbone having appended thereto at least one carbamate functionalgroup, and a second component comprising a compound having a pluralityof functional groups that are reactive with said carbamate groups.

However, regardless of the foregoing improvements, the application of aclear coating composition over a colored basecoat in a wet-on-wet or twocoat/one bake system may sometimes result in an undesirable phenomenonknown as "wrinkling".

Wrinkling often manifests as one or more small furrows or ridges in thecured clearcoat. Most often, there appears a plurality of furrows, oftenin areas of low clearcoat film build and high basecoat film build. It istheorized that such imperfections are caused by folding or "wrinkling"of the clearcoat during the curing process.

While not wishing to be bound to a particular theory, it is believedthat wrinkling may occur as a result of the presence of or reactionbetween volatilized amines and acid catalysts. Such a combination canresult from the use of a basecoat composition employing waterbornetechnology, especially anionically stabilized waterborne technology,requiring the use of volatile amines and a solvent borne clearcoatcomposition utilizing strong acid catalyzed melamine formaldehydecrosslinkers.

Cured color-plus-clear composite coatings exhibiting wrinkling do notpossess the required appearance and/or degree of clarity. Compositecoatings vulnerable to wrinkling are viewed unfavorably by theautomotive industry.

Thus, there is a need for a curable coating composition suitable for usein a color-plus-clear composite coating which possesses desirablecuring, performance, and appearance properties but which does notexhibit wrinkling upon cure of the composite coating.

Desirable performance properties in a composite coating are good solventresistance, hardness and environmental etch resistance. The compositecoating and components thereof should also cure at commerciallyacceptable curing conditions. Advantageous appearance properties in acomposite coating and the components thereof are a color resultingsolely from the desired pigmentation, high DOI, and a glossy appearanceover a wide range of basecoat and clearcoat film thickness.

In particular, it would be advantageous to provide curable coatingcompositions comprising carbamate functional resins which, when used ina color-plus-clear composite coating, do not exhibit wrinkling upon cureof the composite coating.

Most particularly, it would be desirable to provide clearcoat coatingcompositions which, when used as the clear in a color-plus-clearcomposite coating, provide composite coatings having advantageous cure,performance and environmental etch properties as well as improvedappearance, such as being substantially free of wrinkling.

Finally, it would be desirable to provide a method for providingsubstantially wrinkle free color-plus-clear composite systems.

SUMMARY OF THE INVENTION

It is thus an objective of the invention to provide a curable coatingcomposition and a method for using the same to produce color-plus-clearcomposite coatings which have advantageous performance and appearanceproperties and which are substantially free of wrinkling upon cure.

More particularly, it is an objective of the invention to providecurable coating compositions comprising a first component which is acompound having appended thereto at least one carbamate or ureafunctional group, or a group convertible to a carbamate or urea group,and a second component which is a compound reactive with said carbamateor urea groups on component (a), which coating compositions do notexhibit wrinkling when used as the clearcoat in a color-plus-clearcomposite coating.

It has now been unexpectedly discovered that the foregoing can beachieved with the use of a particular curable coating compositionincluding a film forming component (A) which includes a first component(a) comprising a compound having appended thereto at least one carbamateor urea functional group, or a group convertible to a carbamate or ureagroup, and a second component (b) comprising a compound reactive withsaid carbamate or urea groups on component (a), a second component (B)comprising a cyclic anhydride, and a catalyst (C). It has unexpectedlybeen found that a second coating comprising the combination of (B) and(C) provides a cured composite coating having desirable performanceproperties and greatly reduced wrinkling.

The method of the invention achieves the foregoing objectives byapplying a first coating to a substrate, applying a second coating tothe first coating to provide a composite coating, the second coatingcomprising a film forming component (A) which includes a first component(a) comprising a compound having appended thereto at least one carbamateor urea functional group, or a group convertible to a carbamate or ureagroup, and a second component (b) comprising a compound reactive withsaid carbamate or urea groups on component (a), a second component (B)comprising a cyclic anhydride, and a catalyst (C), and subjecting thecomposite coating to a temperature between 170° F./76.6° C. and 350°F./176.6° C. for a time sufficient to effect cure of the compositecoating, wherein the cured composite coating is substantially wrinklefree. More preferably, second component (B) will comprise a cyclicnonaromatic anhydride and most preferably a cyclic anhydride having nounsaturation in either the cyclic anhydride ring or substituentsthereto.

DETAILED DESCRIPTION

The present inventions provide a curable coating composition for use inobtaining color-plus-clear composite coatings having improved appearancewith respect to wrinkling and color, and a method of providing suchcured composite coatings.

The curable coating composition of the invention comprises a filmforming component (A), a second component (B) comprising a cyclicanhydride, and a catalyst (C).

The term "film forming component (A)" as used herein refers to thebinder or solid material which forms the polymeric film portion of thecured film. Film forming component (A) of the curable coatingcomposition of the invention includes a first component (a) whichcomprises a compound having appended thereto at least one carbamate orurea functional group, or a group convertible to a carbamate or ureagroup and a second component (b) comprising a compound reactive withsaid carbamate or urea groups on component (a).

First component (a) comprises a compound selected from the groupconsisting of oligomers and polymers having appended thereto more thanone carbamate group or more than one urea group, or more than one groupconvertible to a carbamate or urea group.

Oligomers typically have a molecular weight of between 148 and 2000, thepreferred molecular weight for the oligomers is between 900 and 1092;polymers typically have a molecular weight of between 2,000 and 20,000,the preferred molecular weight for the polymers is between 4000 and6000. Mixtures of said oligomers and polymers may be used as component(A). Molecular weight can be determined by the GPC method using apolystyrene standard. The carbamate or urea content of the polymer, on amolecular weight per equivalent of carbamate or urea functionality, willgenerally be between 200 and 1200, and preferably between 300 and 800.

Carbamate groups can generally be characterized by the formula ##STR1##wherein R is H or alkyl, preferably of 1 to 4 carbon atoms. Preferably,R is H or methyl, and more preferably R is H.

Urea groups can generally be characterized by the formula ##STR2##wherein R' and R" each independently represent H or alkyl, preferably of1 to 4 carbon atoms, or R' and R" may together form a heterocyclic ringstructure (e.g. where R' and R" form an ethylene bridge).

Groups that can be converted to carbamate include cyclic carbonategroups, epoxy groups, and unsaturated bonds. Cyclic carbonate groups canbe converted to carbamate groups by reaction with ammonia or a primaryamine, which ring-opens the cyclic carbonate to form a β-hydroxycarbamate. Epoxy groups can be converted to carbamate groups by firstconverting to a cyclic carbonate group by reaction with CO₂. This can bedone at any pressure from atmospheric up to supercritical CO₂ pressures,but is preferably under elevated pressure (e.g. 60-150 psi). Thetemperature for this reaction is preferably 60-150° C. Useful catalystsinclude any that activate an oxirane ring, such as tertiary amine orquaternary salts (e.g. tetramethyl ammonium bromide), combinations ofcomplex organotin halides and alkyl phosphonium halides (e.g., ((CH)₃SnI, BU₄ SnI, Bu₄ PI, and (CH₃)₄ PI), potassium salts (e.g., K₂ CO₃,KI), preferably in combination with crown ethers, tin octoate, calciumoctoate, and the like. The cyclic carbonate group can then be convertedto a carbamate group as described above. Any unsaturated bond can beconverted to carbamate groups by first reacting with peroxide to convertto an epoxy group, then with CO₂ to form a cyclic carbonate, and thenwith ammonia or a primary amine to form the carbamate.

Oligomeric compounds useful as first component (a), and having more thanone carbamate functional group, have the general formula ##STR3##wherein X is O, S or NH, R₁ is H or alkyl of 1 to 4 carbon atoms. Thecompounds useful as oligomeric component (a) according to the inventioncan be prepared in a variety of ways.

The carbamate can be primary, terminating in an NH₂ group, or secondary,terminating in an NHR group. In a preferred embodiment, the carbamate isprimary.

One way to prepare oligomeric compounds useful as component (a) is toreact an alcohol (`alcohol` is defined herein as having one or more OHgroups) with more than one urea to form a compound with carbamategroups. This reaction is accomplished by heating a mixture of thealcohol and ureas. This reaction is also performed under heat,preferably in the presence of a catalyst as is known in the art. Anothertechnique is the reaction of an alcohol with cyanic acid to form acompound with primary carbamate groups (i.e., unsubstituted carbamates).Carbamates may also be prepared by reaction of an alcohol with phosgeneand then ammonia to form a compound having primary carbamate groups, orby reaction of an alcohol with phosgene and then a primary amine to forma compound having secondary carbamate groups. Another approach is toreact an isocyanate (e.g., HDI, IPDI) with a compound such ashydroxypropyl carbamate to form a carbamate-capped isocyanatederivative. Finally, carbamates can be prepared by a transcarbamylationapproach where an alcohol is reacted with an alkyl carbamate (e.g.,methyl carbamate, ethyl carbamate, butyl carbamate) to form a primarycarbamate group-containing compound. This reaction is performed underheat, preferably in the presence of a catalyst such as an organometalliccatalyst (e.g., dibutyltin dilaurate). Other techniques for preparingcarbamates are also known in the art and are described, for example, inP. Adams & F. Baron, "Esters of Carbamic Acid", Chemical Review,v. 65,1965.

Various alcohols can be used in the preparation of carbamate compoundsuseful as first component (a) according to the invention. They generallyhave from 1 to 200 carbon atoms, preferably 1-60 carbon atoms, and maybe monofunctional or polyfunctional (preferably a functionality of 2 to3), aliphatic, aromatic, or cycloaliphatic. They may contain just OHgroups, or they may contain OH groups plus heteroatoms such as O, S, Si,N, P, and other groups such as ester groups, ether groups, amino groups,or unsaturated sites. Examples of useful alcohols include1,6-hexanediol,1,2-hexanediol, 2-ethyl-1,3-hexanediol,ethyl-propyl-1,5-pentanediol, 2-methyl-2,4-pentanediol,2,2,4-trimethyl-1,3-pentanediol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol,1,3-dihydroxyacetone dimer, 2-butene-1,4-diol, pantothenol,dimethyltartrate, pentaethylene glycol, dimethyl silyl dipropanol, and2,2'-thiodiethanol.

Polymeric compounds suitable for use in first component (a) are selectedfrom the group consisting of polyester, epoxy, alkyd, urethane, acrylic,polyamide, and polysilane polymers and mixtures thereof, wherein thepolymer has more than one carbamate functional group appended thereto.

In a preferred embodiment, first component (a) comprises a carbamatefunctional acrylic polymer represented by the randomly repeating unitsaccording to the following formula: ##STR4##

In the above formula, R represents H or CH₃. R' represents H, alkyl,preferably of 1 to 6 carbon atoms, or cycloalkyl, preferably up to 6ring carbon atoms. It is to be understood that the terms alkyl andcycloalkyl are to include substituted alkyl and cycloalkyl, such ashalogen-substituted alkyl or cycloalkyl. Substituents that will have anadverse impact on the properties of the cured material, however, are tobe avoided. For example, ether linkages are thought to be susceptible tophoto-induced hydrolysis, and should be avoided in locations that wouldplace the ether linkage in the crosslink matrix. The values x and yrepresent weight percentages, with x being 10 to 90% and preferably 20to 50%, and y being 90 to 10% and preferably 80 to 50%.

In the formula, A represents repeat units derived from one or moreethylenically unsaturated monomers. Such monomers for copolymerizationwith acrylic monomers are known in the art. They include alkyl esters ofacrylic or methacrylic acid, e.g., ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate, butyl methacrylate, isodecyl methacrylate,hydroxyethyl methacrylate, hydroxypropyl acrylate, and the like; andvinyl monomers such as unsaturated m-tetramethyl xylene isocyanate (soldby American Cyanamid as TMI®), vinyl toluene, styrene, styrenicderivatives such as α-methyl styrene, t-butyl styrene, and the like.

L represents a divalent linking group, preferably an aliphatic of 1 to 8carbon atoms, cycloaliphatic, or aromatic linking group of 6 to 10carbon atoms. Examples of L include ##STR5## --(CH₂)--, --(CH₂)₂ --,--(CH₂)₄ --, and the like. In one preferred embodiment, --L-- isrepresented by --COO--L'-- where L' is a divalent linking group. Thus,in a preferred embodiment of the invention, polymeric first component(a) is represented by randomly repeating units according to thefollowing formula: ##STR6##

In this formula, R, R', A, x, and y are as defined above. L' may be adivalent aliphatic linking group, preferably of 1 to 8 carbon atoms,e.g., --(CH₂)--, --(CH₂)₂ --, --(CH₂)₄ --, and the like, or a divalentcycloaliphatic linking group, preferably up to 8 carbon atoms, e.g.,cyclohexyl, and the like. However, other divalent linking groups can beused, depending on the technique used to prepare the polymer. Forexample, if a hydroxyalkyl carbamate is adducted onto anisocyanate-functional acrylic polymer, the linking group L' wouldinclude an --NHCOO-- urethane linkage as a residue of the isocyanategroup. This carbamate functional acrylic polymer is described in U.S.Pat. No. 5,356,669 which is hereby incorporated by reference.

The first component (a) polymer used in the composition of the inventioncan be prepared in a variety of ways. One way to prepare such polymersis to prepare an acrylic monomer having a carbamate functionality in theester portion of the monomer. Such monomers are well-known in the artand are described, for example in U.S. Pat. Nos. 3,479,328, 3,674,838,4,126,747, 4,279,833, and 4,340,497, the disclosures of which areincorporated herein by reference. One method of synthesis involvesreaction of a hydroxy ester with urea to form the carbamyloxycarboxylate (i.e., carbamate-modified acrylic). Another method ofsynthesis reacts an a,b-unsaturated acid ester with a hydroxy carbamateester to form the carbamyloxy carboxylate. Yet another techniqueinvolves formation of a hydroxyalkyl carbamate by reacting ammonia, or aprimary or secondary amine or diamine with a cyclic carbonate such asethylene carbonate. The hydroxyl group on the hydroxyalkyl carbamate isthen esterified by reaction with acrylic or methacrylic acid to form themonomer. Other methods of preparing carbamate-modified acrylic monomersare described in the art, and can be utilized as well. The acrylicmonomer can then be polymerized along with otherethylenically-unsaturated monomers, if desired, by techniques well-knownin the art.

An alternative route for preparing an acrylic polymer for use ascomponent (a) in the composition of the invention is to react analready-formed polymer such as an acrylic polymer with another componentto form a carbamate-functional group appended to the polymer backbone,as described in U.S. Pat. No. 4,758,632, the disclosure of which isincorporated herein by reference. One technique for preparing suchacrylic polymers involves thermally decomposing urea (to give offammonia and HNCO) in the presence of a hydroxy-functional acrylicpolymer or co-polymer to form a carbamate-functional acrylic polymer.Another technique involves reacting the hydroxyl group of a hydroxyalkylcarbamate with the isocyanate group of an isocyanate-functional acrylicor vinyl monomer to form the carbamate-functional acrylic.Isocyanate-functional acrylics are known in the art and are described,for example in U.S. Pat. No. 4,301,257, the disclosure of which isincorporated herein by reference. Isocyanate vinyl monomers arewell-known in the art and include unsaturated m-tetramethyl xyleneisocyanate (sold by American Cyanamid as TMI®). Yet another technique isto react the cyclic carbonate group on a cyclic carbonate-functionalacrylic with ammonia in order to form the carbamate-functional acrylic.Cyclic carbonate-functional acrylic polymers are known in the art andare described, for example, in U.S. Pat. No. 2,979,514, the disclosureof which is incorporated herein by reference. A more difficult, butfeasible way of preparing the polymer would be to trans-esterify anacrylate polymer with a hydroxyalkyl carbamate.

Groups capable of forming urea groups include amino groups that can beconverted to urea groups by reaction with a monoisocyanate (e.g., methylisocyanate) to form a secondary urea group or with cyanic acid (whichmay be formed in situ by thermal decomposition of urea) to form aprimary urea group. This reaction preferably occurs in the presence of acatalyst as is known in the art. An amino group can also be reacted withphosgene and then ammonia to form a compound having primary ureagroup(s), or by reaction of an amino group with phosgene and then aprimary amine to form a compound having secondary urea groups. Anotherapproach is to react an isocyanate with a hydroxy urea compound to forma urea-capped isocyanate derivative. For example, one isocyanate groupon toluene diisocyanate can be reacted with hydroxyethyl ethylene urea,followed by reaction of the other isocyanate group with an excess ofpolyol to form a hydroxy carbamate.

Second component (b) comprises a compound having functional groupsreactive with said carbamate or urea groups on component (a). Suitablereactive groups include active methylol or methylalkoxy groups onaminoplast crosslinking agents or on other compounds such asphenol/formaldehyde adducts, acrylamide groups, isocyanate groups,siloxane groups, cyclic carbonate groups, and anhydride groups. Examplesof (b) compounds include melamine formaldehyde resin (includingmonomeric or polymeric melamine resin and partially or fully alkylatedmelamine resin), urea resins (e.g., methylol ureas such as ureaformaldehyde resin, alkoxy ureas such as butylated urea formaldehyderesin), polymers having acrylamide groups, polymers having methylol oralkoxymethyl groups, polyanhydrides (e.g., polysuccinic anhydride), andpolysiloxanes (e.g., trimethoxy siloxane). Aminoplast resin such asmelamine formaldehyde resin or urea formaldehyde resin are especiallypreferred. Even more preferred are aminoplast resins where one or moreof the amino nitrogens is substituted with a carbamate group for use ina process with a curing temperature below 150° C., as described in U.S.patent application Ser. No. 07/965,510 entitled"Carbamate-Defunctionalized Aminoplast Curing for Polymer Compositions"in the names of John W. Rehfuss and Donald L. St. Aubin.

The curable coating composition of the invention further requires theuse of component (B) and catalyst (C). It has unexpectedly been foundthat the combination of particular component (B) and catalyst (C)provides a second coating, which when used in the method of theinvention, results in a cured composite coating having improvedappearance, especially with respect to wrinkling, in conjunction withdesirable performance properties. This has been found to be the caseeven the first coating is an anionically stabilized water bornebasecoat.

Second component (B) comprises a cyclic anhydride. Cyclic anhydrideswhich are soluble in one or more alcohols are especially suitable foruse as component (B). More preferably, second component (B) willcomprise a cyclic nonaromatic anhydride and most preferably, a cyclicanhydride having no unsaturation in either the cyclic anhydride ring orsubstituents thereto.

Examples of illustrative components (B) are succinic anhydride, glutaricanhydride and methyl hexahydrophthalic anhydride. Succinic anhydride ismost preferred in combination with a suitable catalyst (C). Asillustrated in the examples, it has been found that anhydridescontaining unsaturation in the anhydride ring or substituents thereto,such as phthalic anhydride, do not provide the desired cure ornonwrinkling appearance in conjunction with catalyst (C).

It has been found that second component (B) should be present in amountof from 2.5 to 10.0 percent by weight, based on the total nonvolatile offilm forming component (A). Preferably, it has been found that whencomponent (B) is succinic anhydride, (B) should be present in an amountof at least 3% by weight, based on the total nonvolatile of film formingcomponent (A). More preferably, it has been found that when component(B) is succinic anhydride, (B) will be present in an amount of from 3.5to at least 7% by weight, based on the total nonvolatile of film formingcomponent (A).

Suitable catalysts (C) are those traditional catalysts used to enhancethe cure reaction such as strong acid catalysts. Although such catalystshave been known to produce wrinkling, it has been found that thecombination of (B) and (C) provides excellent cure without wrinkling.

Suitable catalysts (C) include, for example, p-toluenesulfonic acid,dinonylnaphthalene disulfonic acid, dodecylbenzenesulfonic acid, phenylacid phosphate, monobutyl maleate, butyl phosphate, and hydroxyphosphate ester. Catalyst (C) may be blocked, for example with asuitable amine. Examples of suitable blocked catalysts are Nacure™ 5528catalyst and Nacure™ 5543 catalyst, both of which are amine blockeddodecylbenzenesulfonic acid, commercially available from King Industriesof Norwalk, Conn. A most preferred example of a nonblocked strong acidcatalyst is dodecylbenzenesulfonic acid (DDBSA).

A coating composition according to the present invention may beutilized, for example, in the form of substantially solid powder, or adispersion, and optionally solvent may be utilized in the composition ofthe present invention. It is often desirable that the composition is ina substantially liquid state, which can be accomplished with the use ofa solvent. In general, depending on the solubility characteristics ofcomponent (A) and (B), the solvent can be any organic solvent and/orwater. In a preferred embodiment, the solvent comprises at least onepolar organic solvent. More preferably, the solvent is a polar aliphaticsolvent. Still more preferably, the solvent is a ketone, ester, acetate,alcohol, aprotic amide, aprotic sulfoxide, aprotic amine and mixturesthereof. The use of at least one alcohol is especially preferred.Examples of useful solvents include ethanol, isobutanol (iBuOH),methanol (MeOH), propylene carbonate (PC), methyl ethyl ketone, methylisobutyl ketone, n-amyl acetate, ethylene glycol butyl ether-acetate,propylene glycol monomethyl ether acetate, xylene, n-methylpyrrolidone,blends of aromatic hydrocarbons, and mixtures thereof. Alternatively,the solvent may be water or a mixture of water with small amounts ofaqueous co-solvents.

Additional ingredients may be added to the coating composition, such as,but not limited to pigments, rheology control agents, flow controladditives, ultraviolet absorbers, and hindered amine light stabilizers.

In a preferred embodiment of the invention, the composition of theinvention is utilized as a pigmented coating composition or clearcoatcoating composition. In such a composition, the solvent may be presentin the composition of the invention in an amount of from about 0.01weight percent to about 99 weight percent, preferably from about 10weight percent to about 60 weight percent, and more preferably fromabout 30 weight percent to about 50 weight percent.

In a particularly preferred embodiment, the composition of the inventionis used as a clear and/or colorless coating composition over a pigmentedbasecoat as part of a composite color-plus-clear coating. Such compositecoatings are popular for their depth of color and liquid glossy surfaceappearance. They have found particularly wide acceptance in the field ofautomotive coatings. The composition of the invention may also be usedas the basecoat of a composite color-plus-clear coating.

The invention further provides a method for providing a compositecoating having an improved appearance, especially with respect towrinkling. The method requires that a first coating be applied to asubstrate.

The first coating will generally be a cured composition, such as aprimer, basecoat or clearcoat composition. Preferably, the first coatingwill be a pigmented basecoat composition, and most preferably a waterborne basecoat composition such as is described in U.S. Pat. No. Re.34,730, hereby incorporated by reference.

Other pigmented basecoat compositions for such composite coatings arewell-known in the art, and do not require explanation in detail herein.Polymers known in the art to be useful in basecoat compositions includeacrylics, vinyls, polyurethanes, polycarbonates, polyesters, alkyds, andpolysiloxanes. A preferred polymer is an acrylic polymer.

After the first coating is applied to the substrate, a second coating isapplied to the substrate previously coated with the first coating. Thesecond coating is applied directly onto the first coating. Preferablythe second coating is applied to the first coating before the firstcoating is cured. Drying of the first coating short of complete cure mayoccur. The second coating comprises the coating composition of theinstant invention comprising components (A) and (B) discussed above.

Substrates may be plastic, metal, wood and mixtures thereof. Preferredsubstrates are plastic and metal automotive substrates, especially metalautomotive body panels.

Coating compositions can be coated on the article by any of a number oftechniques well-known in the art. These include, for example, spraycoating, dip coating, roll coating, curtain coating, and the like. Forautomotive body panels, spray coating is preferred.

After an article is molded, casted, or coated with the above-describedlayers, the composition is subjected to conditions so as to cure thecoating layers. Although various methods of curing may be used,heat-curing is preferred. Generally, heat curing is effected by exposingthe coated article to elevated temperatures provided primarily byradiative heat sources.

Curing temperatures will vary depending on the composition of first andsecond components (a) and (b)used, however they generally range betweenabout 170° F./77° C. and 395° F./201° C., preferably between 200° F./93°C. and 350° F./177° C., and most preferably between 250° F./121° C. and286° F./141° C. The curing time will vary depending on the particularcomponents used and physical parameters such as the thickness of thelayers, however, typical curing times range from 15 to 60 minutes.

The invention is further described in the following nonlimitingexamples.

EXAMPLE 1

Clearcoat compositions A-C were prepared according to the followingformulations. Composition A was the DDBSA control. All measurements arein grams unless otherwise specified.

                  TABLE 1                                                         ______________________________________                                        Material                                                                              Composition A                                                                              Composition B                                                                            Composition C                                 ______________________________________                                        Resin.sup.1                                                                           150.2        150.0      151.7                                         DDBSA   5.2          5.2        5.2                                           Melamine.sup.2                                                                        18.0         17.9       18.5                                          Succinic                                                                              --           8.0        --                                            Anhydride.sup.3                                                               Phthalic                                                                              --           --         5.0                                           Anhydride.sup.4                                                               NMP     12.4         12.4       12.4                                          amyl acetate                                                                          16.1         16.1       16.1                                          isobutanol                                                                            6.3          6.3        6.3                                           Propylene                                                                             17.2         17.2       17.2                                          Carbonate                                                                     ______________________________________                                         .sup.1 The resin was a carbamate functional acrylic prepared in accordanc     with U.S. Pat. No. 5,356,669, incorporated herein.                            .sup.2 The melamine used was a monomeric methylated melamine.                 .sup.3 The succinic anhydride was in the form of a 50% solution of the        anhydride prepared in propylene carbamate.                                    .sup.4 The phthalic anhydride is in the form of a 25% solution of phthali     anhydride prepared in a 50/50 blend of acetone and propylene carbamate.  

A water borne silver metallic anionically stabilized polyester basedbasecoat was sprayed onto 12"×18" electrocoated steel panels (APR17438)from ACT of Hillsdale, Mich. The basecoat and clearcoat samples wereapplied in a wedge, that is, the basecoat film build varied from 0.2 milat the top of the panel to 0.7 mil at the bottom of the panel. Theclearcoat film build varied from 1.0 mil (left side of panel) to 2.0 mil(right side of panel).

The basecoat was dried for 5 minutes at 120° F., followed by applicationof a clearcoat sample. The clearcoats were flashed for 5 minutes atambient and baked for 20 minutes at 270° F.

All samples were clear in color. Both samples B and C passed an MEK soaktest and had over 200 rubs on the MEK double rub test. Sample B,(succinic anhydride) did not show any wrinkling, while sample C(phthalic anhydride) did wrinkle. Although poor cure was observed on oneedge of the sample B panel, it is believed that this is due to a coldspot in the oven.

EXAMPLE 2

An experiment to determine the correct amount of component (B) wasconducted. Varying levels of succinic anhydride were added to URECLEAR®clearcoat, a commercially available solvent borne carbamatedacrylic/melamine based clearcoat sold by BASF Corporation, Southfield,Mich. The % succinic anhydride was based on the total nonvolatile offilm forming component (A).

Sample panels were prepared as in Example 1.

                  TABLE 2                                                         ______________________________________                                                                        Tukon                                                                Tukon    Hardness                                      % Succinic             Hardness.sup.5                                                                         Composite                                     Anydride  % Wrinkle    Clearcoat                                                                              Coating                                       ______________________________________                                        0%        75           6.8      4.5                                           0.9%      75           9.1      4.3                                           1.7%      25           7.8      4.1                                           3.5%      ≈5   7.9      2.9                                           7.0%      0            8.4      2.2                                           ______________________________________                                         .sup.5 Tukon Hardness in Knoops according to ASTM D1474.                 

The results indicated that the presence of at least 1.0 to 2.0 percentsuccinic anhydride produced significant reduction in wrinkling in asolvent borne clearcoat applied over a water borne anionicallystabilized basecoat.

EXAMPLE 3

The effect of certain cyclic anhydrides with blocked acids wasinvestigated. A first sample (A) was prepared by combining about 300grams of the resin used in Example 1, about 35 grams of the melamineused in Example 1 and about 10.5 grams of Nacure™ 5528 catalyst⁶.Approximately 80 to 100 grams of the solvent blend used in Example 1 wasalso added.

A second sample (B) was similarly prepared but about 10.5 grams ofNacure™ 5543 catalyst⁷ was used in place of the Nacure™ 5528 catalyst.

Sample A was divided into 3 equal samples, A1, A2, and A3. Sample B wasdivided into 3 equal samples, B1, B2, and B3. Four samples, (A1, A2, B1,and B2) were used to make the following compositions.

                  TABLE 3                                                         ______________________________________                                                 C1   C2          C3     C4                                           ______________________________________                                        A1         100                                                                A2                100                                                         B1                            100                                             B2                                 100                                        Succinic   --      7%         --    7%                                        Anhydride                                                                     ______________________________________                                    

Sample panels were prepared according to the manner of Example 1, exceptthat APR26073 10"×10" steel panels from ACT of Hillsdale, Mich. wereused.

The results are set forth below in Table 4.

                  TABLE 4                                                         ______________________________________                                                 Clearcoat                                                                              Basecoat                                                    Sample   Tukon    Tukon       Wrinkle                                                                             Yellowing                                 ______________________________________                                        C1       7.67     6.5         YES   NO                                        C2       9.33     8.65        NO    NO                                        C3       8.11     8           YES   NO                                        C4       7.7      6.9         NO    NO                                        ______________________________________                                    

The samples according to the invention did not wrinkle.

EXAMPLE 4

The effect of hexahydromethylphthalic anhydride (HHMPA) on wrinkling wasinvestigated. About 11 grams of DDBSA and 31.1 grams of HHMPA were addedto approximately 500 of URECLEAR® clearcoat made without catalyst.URECLEAR® clearcoat is a commercially available solvent borne carbamatedacrylic/melamine based clearcoat sold by BASF Corporation, Southfield,Mich. The sample was reduced to about 32 seconds on a #4 Ford viscositycup using a 1:1 blend of oxo-hexyl acetate and methyl isoamyl ketone.

A sample panel was prepared according to the manner of Example 1. Nowrinkling was observed.

What is claimed is:
 1. A method for providing a composite coating havingan improved appearance, comprising:applying a first coating to asubstrate; applying a second coating to the first coating to provide acomposite coating, the second coating comprising,(A) a film formingcomponent comprising(a) a first component comprising a compound havingappended thereto at least one carbamate or urea functional group, or agroup convertible to a carbamate or urea group, and (b) a secondcomponent comprising a compound reactive with said carbamate or ureagroups on component (a), (B) a cyclic anhydride having no unsaturationin either the cylic anhydride ring or substituents thereto, and (C) acatalyst, and subjecting the composite coating to a temperature betweenabout 170° F./77° C. to 350° F./177° C. for a time sufficient to providea cured composite coating, the cured composite coating having animproved appearance relative to a composite coating having a secondcoating free of component (B).
 2. The method of claim 1 wherein thecured composite coating is substantially wrinkle free.
 3. The method ofclaim 1 wherein first component (a) comprises a compound selected fromthe group consisting of oligomers having appended thereto more than onefunctional group selected from the group consisting of carbamate groups,urea groups and groups converted to carbamate or urea groups, saidoligomers having a molecular weight of between 148 and 2000, polymershaving appended thereto more than one functional group selected from thegroup consisting of carbamate groups, urea groups and functional groupsconvertible to carbamate or urea groups, said polymers having amolecular weight of greater than 2000, and mixtures of said polymers andoligomers.
 4. The method of claim 1 wherein said first component (a)comprises a carbamate or urea functional polymer selected from the groupconsisting of polyester, epoxy, alkyd, urethane, acrylic, polyamide andpolysilane polymers and mixtures thereof.
 5. The method of claim 3wherein first component (a) comprises a polymer backbone having appendedthereto more than one carbamate functional group, said first componentbeing represented by randomly repeating units according the formula:##STR7## R represents H or CH₃, R' represents H, alkyl, or cycloalkyl,Lrepresents a divalent linking group, A represents repeat units derivedfrom one or more ethylenically unsaturated monomers, x represents 10 to90 weight %, and y represents 90 to 10 weight %.
 6. The method of claim5 wherein A represents repeat units derived from more than oneethylenically unsaturated monomers, more than one monomer havingappended thereto a carbamate group.
 7. The method of claim 5, wherein Arepresents repeat units derived from one or more ethylenicallyunsaturated monomer, said ethylenically unsaturated monomers comprisingone or more acrylic monomers.
 8. The method of claim 7 wherein 10-90% byweight of said ethylenically unsaturated monomers are acrylic monomers.9. The method of claim 5 wherein --L-- is represented by the formula--COO--L', where L' is a divalent linking group.
 10. The method of claim1 wherein first component (a) comprises an oligomer having appendedthereto more than one functional group selected from the groupconsisting of carbamate groups, urea groups, and groups subsequentlyconverted to carbamate or urea groups, said oligomer having a molecularweight of between 148 and
 2000. 11. The method of claim 1, whereinsecondcomponent (b) comprises a compound selected from the group consisting ofmelamine formaldehyde resins, urea resins, polymers having acrylamidegroups, polymers having methylol or alkoxymethyl groups, polyanhydridesand polysiloxanes.
 12. The method of claim 11, wherein second component(b) comprises a compound selected from the group consisting of melamineformaldehyde resins and urea resins.
 13. The method of claim 1, whereinthe cyclic anhydride is selected from the group consisting of succinicanhydride, glutaric anhydride, methyl hexahydrophthalic anhydride andmixtures thereof.
 14. The method of claim 13, wherein the cyclicanhydride is succinic anhydride.
 15. The method of claim 13, wherein thecyclic anhydride is methyl hexahydrophthalic anhydride.
 16. The methodof claim 14, wherein the second coating comprises at least 2% by weightof succinic anhydride, based on the nonvolatile portion of film formingcomponent (A).
 17. The method of claim 1, wherein the second coatingfurther comprises(C) one or more solvents, (D) additives, and (E)optionally, pigments.
 18. The method of claim 1 wherein the firstcoating is a pigment containing basecoat.
 19. The method of claim 18wherein the first coating is a water borne pigment containing basecoat.20. The method of claim 1 wherein the second coating is a solvent bornecoating.
 21. The method of claim 20 wherein the second coating isclearcoat.
 22. The method of claim 1 wherein the second coating furthercomprises dodecylbenzenesulfonic acid as catalyst (C).
 23. The method ofclaim 1 comprising subjecting the composite coating to a temperaturebetween 220° F./104.4° C. and 300° F./148.9° C.
 24. The method of claim23 comprising subjecting the composite-coating to a temperature between240° F./115.6° C. and 280° F./137.8° C. for a time between 18 to 25minutes.
 25. The method of claim 1 wherein the first coating is notcured prior to the application of the second coating.
 26. A method forproviding a composite coating comprising:applying a first coating to asubstrate; applying a second coating to the first coating to provide acomposite coating, the second coating comprising,(A) a film formingcomponent comprising(a) a first component comprising a compound havingappended thereto at least one carbamate or urea functional group, or agroup convertible to a carbamate or urea group, and (b) a secondcomponent comprising a compound reactive with said carbamate or ureagroups on component (a), (B) a cyclic anhydride having no unsaturationin either the cylic anhydride ring or substituents thereto, and (C) acatalyst, and subjecting the composite coating to a temperature betweenabout 170° F./77° C. to 350° F./177° C. for a time sufficient to providea cured composite coating.
 27. A curable coating compositioncomprising,(A) a film forming component comprising(a) a first componentcomprising a compound having appended thereto at least one carbamate orurea functional group, or a group convertible to a carbamate or ureagroup, and (b) a second component comprising a compound reactive withsaid carbamate or urea groups on component (a), and (B) a cyclicanhydride having no unsaturation in either the cylic anhydride ring orsubstituents thereto, and (C) a catalyst.